oscilloscope

Hi,
i’ve been trying to make a simple oscilloscope with the jit.poke~ object.
The problem i’m encountering at the moment is some sort of vertical scanline / offset distortion in the image.
I attached the patch, hope somebody knows how to solve this.
Many thanx
Lev

— Pasted Max Patch, click to expand. —

Copy all of the following text. Then, in Max, select New From Clipboard.